Automated data storage libraries are known for providing cost effective access to large quantities of stored data. Generally, data storage libraries include a large number of storage slots in which are stored portable data storage media. The typical portable data storage medium is a tape cartridge or an optical cartridge. An accessor typically accesses the data storage media from the storage slots and delivers the accessed media to a data recording device for reading and/or writing data on the accessed media. Suitable electronics both operate the accessor and operate the data recording devices to transmit and/or receive data from an attached on-line host computer system.
In a conventional automated data storage library, the storage slots are arranged in a planar orthogonal arrangement forming a "wall" of storage slots for holding data storage media. The plane may be a flat plane, or may be a cylindrical plane. To double the storage capacity, two "walls" of storage slots may be provided on either side of the accessor.
A number of different companies manufacture automated data storage libraries today, each model displaying various different features. One example is the IBM 3494 Data Storage Library. Some of the automated data storage libraries have dual or multiple accessors to provide a level of redundancy, in that, one accessor is the "active" accessor and the other is a "spare". Thus, if the active accessor fails, another may take over the accessor function and be the active accessor.
Conventionally, one of the accessors is always the active accessor, and the other(s) are always spare. For example, in a dual accessor automated data storage library, the accessors are typically located at opposite ends of an aisle (between the parallel walls of storage slots). One of the accessors is at the "A" end of the aisle and is typically the active accessor, and the other accessor is at the opposite "B" end of the aisle and is typically the standby accessor. The only time that the accessors are switched is when the active accessor fails.